The present invention relates to a DC superconducting quantum interference device ("DC SQUID"), which is applied to a highly sensitive magnetic sensor, an ammeter, a displacement meter, a high-frequency signal amplifier or the like.
The prior art DC SQUID, which is in a top plan view shown in FIG. 2, has a washer cover 8. Its operation is, however, unstable due to the lack of a ground plane, because interlinkage in an external magnetic flux often occurs, tending to invite a trap in the magnetic flux.
Because the trap of interlinkage in the magnetic flux is generated in the neighborhood of a Josephson junction 1, the operation of a conventional DC SQUID is unstable.